Numerous devices have been utilized in the past for infusing drugs or other liquid solutions to persons requiring extended exposure to such solutions. In order to avoid the operational complexities associated with externally powered pumping devices, a great deal of inventive effort has been focused on devices having internally powered mechanical delivery mechanisms.
One concept that has received considerable attention involves the use of a deformable bladder such as that disclosed in U.S. Pat. No. 4,419,096 to Leeper et al. As explained in Leeper, however, a fundamental operational difficulty encountered by the use of a deformable bladder is non-uniformity of operation resulting in a pressure spike near the end of the fluid dispersion cycle. This pressure spike results in a corresponding surge in fluid flow to the patient which is generally undesirable. Leeper addresses this problem by inclusion within the bladder of means to maintain the bladder in a slightly bulbar configuration. The detriment associated with this configuration is, of course, that the medicinal fluid is not completely expelled from the bladder and is therefore wasted. A number of other patents have disclosed configurations utilizing bladders but none appear to have the capability of completely delivering the stored contents at a controlled pressure and flow rate.
To avoid the inherent problems of non-uniform delivery associated with devices such as Leeper, wherein flow is initiated through the collapse of an elastic bladder, a number of alternative concepts have emerged utilizing various driving means to expel the fluid contained in the infusion device. These include inter alia, the spring loaded piston of Turner et al. U.S. Pat. No. 4,248,223, the osmotic pump disclosed in Faste U.S. Pat. No. 4,898,582 and the introduction of pressurization means to aid in the collapse of a rolling diaphragm as disclosed in LaBruna U.S. Pat. No. 4,437,590. Several devices have attempted to avoid the need for a separate driving means to expel the fluid from the apparatus through use of stretched elastomeric membranes. Elastically driven devices are exemplified in Kriesel U.S. Pat. No. 5,019,047 and di Palma et al. U.S. Pat. No. 4,968,301. Kriesel discloses an apparatus for infusing medicinal fluids into a patient at specific rates over extended periods of time. The driving force to expel the fluid contained in the apparatus is provided by the relief of internal stresses created through the stretching of an elastically deformable membrane. The flow-rate of the fluid thereby expelled is controlled by a thin fluid permeable member 26. Similarly, di Palma also utilizes the force generated from an elastically stretched membrane to expel the medicinal fluid.
It is noteworthy that in relying on force generated by a stretched membrane, both Kriesel and di Palma operate in a manner which is fundamentally different from the present invention. While the membranes in Kriesel and di Palma must be stretched, thereby placing significant stresses on components within the infuser and giving rise to enhanced potential for malfunction and breakage, force relied on in the present invention is primarily the bending force derived from a bendably deformable member.
Despite the existence of infusion devices which are capable of delivering fluids at a specific rate over an extended period of time, there remains a need for a simple infusion device which overcomes the deficiency of those devices which are dependent on the use of stretched elastic members, without resorting to external control methods such as those commonly taught and utilized in the art. Specifically, there is a need for a simple, effective infusion device which does not place great stress on the infuser components due to stretching of a diaphragm member. There is also a need for a simple device which is capable of delivering fluids at either constant or variable controlled flow rates without relying on external flow control mechanisms and which may be coupled to similar devices to deliver a plurality of fluids either simultaneously or at staged intervals.